Bst remove

void TREE::usuwanie(NODE*&el){
//  cout << "usuwanie elementu " << el->val << endl;
    if(el->right == NULL && el->left == NULL){
        if(el->parent == NULL){
            root = NULL;
        }
        else if(el->parent->left == el){
            el->parent -> left = NULL;
        }
        else{
            el->parent ->right = NULL;
        }
        delete el;
        return;
    }
    if(el->right!=NULL^el->left!=NULL){
        NODE*tmp;
        if(el->right!=NULL){
            tmp = el->right;
        }
        else{
            tmp=el->left;
        }
        tmp->parent = el->parent;
//      cout << "element tmp: " << tmp->val << endl;
        if(el->parent == NULL){
            root = tmp;
        }
        else if(el->parent->left == el){
            el->parent -> left = tmp;
        }
        else{
            el->parent ->right = tmp;
        }
        delete el;
//      cout << "element tmp po usunieciu: " << endl;
//      tmp->wypisz();
        return;
    }
    NODE*tmp = el->right;
    while(tmp->left != NULL){
        tmp = tmp->left;
    }
    el->val=tmp->val;
    usuwanie(tmp);
}